The present invention relates generally to improvements in cameras and it relates particularly to an improved compact camera self-containing a plurality of objective lenses which are selectively alternatively transferred between displaced and operative positions and a view finder whose field is varied in accordance with the power of the operatively positioned objective lens.
With a camera of the type, in which the power of magnification of the picture-taking or objective lens system is varied by selectively moving two or more objective lenses built or self-retained in the camera into or out of the picture-taking or photographing optical path, it has been necessary to change the picture-taking field or range indicated within the associated view finder in conformity with the selected magnification of the picture-taking lens system.
Mechanisms proposed for changing the picture-taking range indicated within the finder may be classified into two types in which:
(1) The size of a view frame within the finder is changed, while maintaining the magnification of the image in the finder constant, thereby indicating the picture-taking field of the operative picture-taking lens system; and
(2) The magnification of the image in the finder is varied while maintaining the size of the view frame in a finder constant.
According to the first mechanism, the size of the view limiting frame consisting of an Albada finder system alone may be varied, without varying the magnification of the image in the finder, and hence the construction may be simplified. However, in case a picture-taking lens system is changed from a standard lens to a telephoto lens, the size of the view frame of the finder is reduced, and in addition, the finder image is reduced in size, because an object in general is located at a great distance, with the result that detailed observation of the object becomes difficult.
In contrast thereto, the second mechanism is devoid of the aforesaid shortcoming and provides advantages over the first mechanism. However, a complicated structure is required for varying the magnification of the image in the finder, with the resulting increase in the size of the finder as well as in the manufacturing cost.
Moreover, a mechanism has been proposed in which a zoom lens system is employed as a finder optical system for varying the magnification of the image in the field of view of the finder, providing the basic optical system as shown in FIG. 1 of the drawing herein. More particularly, the finder optical system proposed includes an inverse Galilean finder system consisting of a concave objective lens 1 and a convex movable lens 2, a concave lens 3 for use in an Albada finder, and an eye-piece 4, so that the magnification of the image in the finder may be varied by moving the convex movable lens 2 along the system optical axis in the direction of arrows e. In addition, as is well known, the size of the view limiting frame is so arranged as to be maintained constant by means of an optical image frame 4a formed on the object side of eye piece 4, and mirror surface 3a which is formed on the image side of concave Albada lens 3 and shown by a thick line.
In general, important fundamental problems in the finder system are whether or not an optimum magnification is achieved for an image, and how far the image of an object is viewed, when observed in the finder, i.e., a dioptric power problem.
However, with the finder lens system as shown in FIG. 1, when the image magnification of the finder remains substantially unchanged, i.e., in a range lower than 1.5, variation in magnification will not lead to a marked variation in dioptric power, thus providing desired practicability in actual application. However, when the finder magnification is increased to over 1.5, in response to a variation in the magnification of the picture-taking lens, then the variation in the dioptric power will exceed 1 diopter, so that in case the magnification exceeds 2, then the view in the finder becomes hard to recognize, and in addition, marked distortion of the field results, thus failing to provide the desired practicability for a short-sighted photographer who suffers from an insufficient adjusting capability of the eyes.
This may be attributed to the fact that part of the lenses constituting the finder optical system is moved only along the optical axis of a finder, so that compensation for aberration cannot be positively achieved.